1. Field of the Invention
The present invention relates to a small-sized fuel cell system, fuel feed system employed in a polyelectrolyte type fuel cell usable as a power supply for portable electric appliance such as an office automation appliance, in particular, and also to a portable electric appliance.
2. Related Art of the Invention
Generally, a fuel cell induces a chemical reaction between fuel such as hydrogen and oxygen to convert chemical energy directly into electric energy, and therefore a high power generation efficiency is obtained, the noise is very low, and the size can be reduced because there are few mechanical driving parts. Such a fuel cell is relatively easy in installation and management, and is hence used in distributed power supply system, power supply for communication equipment, etc. Recently, a fuel cell system combining fuel cell and hydrogen occlusion alloy has been used as a portable power supply, and various structures have been proposed for such fuel cell system (Japanese Laid-open Patents 6-76848, 6-60894, etc.).
As the fuel, liquid fuel such as methanol, or gas fuel such as natural gas or hydrogen is mainly used, and lately, in particular, as the fuel for small-sized power supply, hydrogen contained in a cylinder filled together with hydrogen occlusion alloy is used because it is relatively easy in handling. For example, in the constitution proposed in Japanese Laid-open Patent 6-150955, a cylinder filled with hydrogen occlusion alloy for feeding hydrogen to the fuel cell is contained in a portable casing independently of the power supply main body containing the fuel cell, and this casing is provided with an exhaust gas inlet for allowing the exhaust gas generated from the fuel cell to pass through the cylinder. In this constitution, since the casing is portable independently of the power supply main body, the casing can be increased in size without space restrictions for containing the cylinder. Moreover, the cylinder temperature and pressure can be elevated by the exhaust gas from the fuel cell, so that the hydrogen can be supplied smoothly.
Moreover, as disclosed in Japanese Laid-open Patent 4-181659, for example, in order to heighten the safety of the fuel cell system, a fuel cell system is proposed, in which the hydrogen equilibrium pressure at the upper limit of the plateau region of hydrogen occlusion alloy as hydrogen storage means is 10 atm or less at ordinary pressure.
On the other hand, portable electronic devices such as laptop computers are extremely reduced in size and weight and enhanced in performance, and as the secondary cells used as power source, high performance cells such as nickel and hydrogen storage battery and lithium ion secondary cells have come to be used from the viewpoint of longer time of use, smaller size and lighter weight.
In the conventional secondary cells, it is difficult to extend the operating time and reduce the size and weight further. Accordingly, it is considered to use the fuel cell in the power source of portable electronic device. In the case of the cylinder filled with such hydrogen occlusion alloy, using hydrogen as fuel, however, the cylinder is required to have a high pressure resistance, and is hence formed in a cylindrical shape, which produces a dead space, and it is disadvantageous for obtaining a long operating time, smaller size and lighter weight.